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Schematic illustration of top down and bottom up methods for the preparation of nanoparticles. 

Schematic illustration of top down and bottom up methods for the preparation of nanoparticles. 

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Article
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X-ray absorption spectroscopy facilitated by state-of-the-art synchrotron radiation technology is presented as a powerful tool to study nanoscale systems, in particular revealing their static element-specific magnetic and electronic properties on a microscopic level. A survey is given on the properties of nanoparticles, nanocomposites and thin film...

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... the preparation of nanoscale systems, different approaches are pursued that can be classified as top down and bottom up methods, respectively, as depicted in figure 1. The former describes the division of a massive solid into smaller portions e.g. by the use of lithographic patterning or milling. ...
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... it is common to measure the x-ray absorption related to core-level electron excitations from 2p 3/2 and 2p 1/2 states into the 3d states (so- called L 3 and L 2 absorption edges, respectively). Electronic transitions into higher unoccupied states or even into the con- tinuum are separated by a two-step-like function from the transitions into the 3d states as shown in figure 10. The height for these two steps reflects the occupation of initial states that is two times higher for the 2p 3/2 states than for the 2p 1/2 states. ...
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... oscillatory behaviour in the extended energy range about 100-1000 eV above the absorption edge, is visible in the absorption signal as can be seen in figure 11. In a simple pic- ture, these oscillations are caused by an interference effect between the outgoing photoelectron as a matter wave and backscattered waves from neighbouring atoms. ...
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... the point of the matter is that in the k-dependence of EXAFS amplitudes, important infor- mation of the type of backscattering atom is included. In figure 12, the Fourier transform and the wavelet transform are shown exemplarily for the EXAFS data presented in fig- ure 11. However the potential to directly visualise contribu- tions of different elemental species is not obvious here, but becomes evident in the example presented in the following subsection. ...
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... the point of the matter is that in the k-dependence of EXAFS amplitudes, important infor- mation of the type of backscattering atom is included. In figure 12, the Fourier transform and the wavelet transform are shown exemplarily for the EXAFS data presented in fig- ure 11. However the potential to directly visualise contribu- tions of different elemental species is not obvious here, but becomes evident in the example presented in the following subsection. ...
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... the following, the main results and conclusions are summarised from the perspective of x-ray absorption. In figure 13 the magnitudes of the FT and the WT are shown for Fe nanopar- ticles synthesised using 2 equivalent diisopropylamine-borane (AeB) as a reducing agent. In this reaction, the reduction of the Fe precursor is accompanied by the reaction of AeB to amino borane (AoB)-containing a BH 2 group instead of the BH 3 in AeB-and H 2 as depicted in figure 14. ...
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... figure 13 the magnitudes of the FT and the WT are shown for Fe nanopar- ticles synthesised using 2 equivalent diisopropylamine-borane (AeB) as a reducing agent. In this reaction, the reduction of the Fe precursor is accompanied by the reaction of AeB to amino borane (AoB)-containing a BH 2 group instead of the BH 3 in AeB-and H 2 as depicted in figure 14. In the total WT ( figure 13(b)), three peaks are clearly vis- ible: one at a radial distance of about 0.14 nm and a wavenum- ber of about 20 nm −1 , the second one at the same wavenumber, but larger radial distance (about 0.21 nm) and the third one at a radial distance of about 0.2 nm and a significantly higher wavenumber of about 60 nm −1 . ...
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... this reaction, the reduction of the Fe precursor is accompanied by the reaction of AeB to amino borane (AoB)-containing a BH 2 group instead of the BH 3 in AeB-and H 2 as depicted in figure 14. In the total WT ( figure 13(b)), three peaks are clearly vis- ible: one at a radial distance of about 0.14 nm and a wavenum- ber of about 20 nm −1 , the second one at the same wavenumber, but larger radial distance (about 0.21 nm) and the third one at a radial distance of about 0.2 nm and a significantly higher wavenumber of about 60 nm −1 . As a reference system, Fe nanoparticles synthesised by hydrogenation without any fur- ther reducing agent were measured yielding the WT shown in figure 13(c). ...
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... the total WT ( figure 13(b)), three peaks are clearly vis- ible: one at a radial distance of about 0.14 nm and a wavenum- ber of about 20 nm −1 , the second one at the same wavenumber, but larger radial distance (about 0.21 nm) and the third one at a radial distance of about 0.2 nm and a significantly higher wavenumber of about 60 nm −1 . As a reference system, Fe nanoparticles synthesised by hydrogenation without any fur- ther reducing agent were measured yielding the WT shown in figure 13(c). Only one peak is obtained that can be assigned to Fe and possible traces of other light elements like oxygen and/ or nitrogen present in the Fe precursor. ...
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... one peak is obtained that can be assigned to Fe and possible traces of other light elements like oxygen and/ or nitrogen present in the Fe precursor. After subtraction of the reference signal, the typical fingerprint of boron is obtained in figure 13(d). ...
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... less AeB as reducing agent for the synthe- sis of Fe nanoparticles leads to less boron incorporated. From the reaction scheme ( figure 14) it is evident that the boron incorporation occured in the second reaction step of the AoB byproduct connected to a further release of H 2 . To gain more insight into the chemical reaction, pre-formed Fe nanoparti- cles prepared by hydrogenation (without any boron) were sub- sequently mixed with AeB at room temperature. ...
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... gain more insight into the chemical reaction, pre-formed Fe nanoparti- cles prepared by hydrogenation (without any boron) were sub- sequently mixed with AeB at room temperature. As described in [145], a fast H 2 evolution was observed evidencing the effi- ciency of these Fe nanoparticles for dehydrogenation of AeB, as depicted in figure 15, step 1. However, the reactivity does not stop with the release of AoB, as incorporation of boron step 2 is revealed from EXAFS measurements. ...
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... a second experiment, AoB was reacted with the preformed Fe nanopar- ticles. Here again, H 2 evolution was observed, thus evidencing the activity of the Fe nanoparticles towards dehydrogenation of the AoB moiety ( figure 15, step 2). The proof of boron incorporation in Fe nanoparticles studied in this work by EXAFS analysis opens a route for the preparation of Fe-B nanoparticles and reveals the property of Fe nanoparticles to dehydrogenate both AeB and AoB derivatives. ...
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... 3 O 4 crystallises in an inverse spinel structure that is depicted in figure 16 ...
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... we pres- ent some multiplet calculation results using the CTM4XAS programme [147] which offers the possibility to calculate the different contributions of different Fe ions to the overall XANES signal site-and valence-specifically. The contribu- tions are shown in figure 17 for Fe 3+ at either O h or tetrahe- dral T d sites and Fe 2+ at O h sites. The crystal field parameters describing the influence of the surrounding oxygen ions were set to 10Dq = 1.5 eV for O h sites and 10Dq = 0.7 eV for T d sites, respectively as suggested in the literature [148,149]. ...
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... spectra were calculated with a Lorentzian broadening of 0.25 eV and a Gaussian broadening of 0.3 eV to account for lifetime effects and finite energy resolution in experiments. It can clearly be seen that the spectral shape for Fe 2+ figure 17, there may be two reasons for the occurrence of a pre-peak feature in the XANES: Fe 2+ ions and Fe 3+ on octahedral sites. The latter yields only a small pre-peak compared to the intensity of the main peak, whereas Fe 2+ yields a more pronounced pre-peak. ...
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... after three days stored in a sealed glass bottle, the Fe 2+ fraction is significantly reduced indicating a fur- ther oxidation of Fe 3 O 4 towards γ-Fe 2 O 3 . Exposure to air gives rise to an even faster oxidation of Fe 3 O 4 nanoparticles in dispersion which is shown in figure 18. These measure- ments have been performed at the HZB-BESSYII synchro- tron radiation facility using the Liquidrom endstation at the U41-PGM beamline. ...
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... addition, Al as a light element produces only a weak background of secondary electrons and, thus, a clear total electron yield signal from the underlying element can be detected. Figure 19 shows a scanning electron microscopy image of FePt nanoparticles with a mean diameter of about 6 nm deposited onto a natu- rally oxidised Si wafer using the spin-coating technique. The particles were synthesised following the wet-chemical route reported by Sun et al [150]. ...
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... the simulations clusters of chemically ordered FePt cuboctahedra covered by a layer of Al, Cu or Au were mod- elled and the system was allowed to relax structurally [35]. The results are visualised in figure 21. It can clearly be seen that capping with Al has a strong influence on the morphology of the nanoparticle, while the structural modifications for Au or Cu capping are only moderate. ...

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